The present disclosure generally relates to implants for, and methods relating to, temporomandibular disorders.
One aspect of the craniomandibular system is that the temporomandibular joint (TMJ) moves in synchrony with its contralateral part. The rotational and translational movements of the TMJ are supported by an intra articular disc. TMJ is thereby a bilateral synovial articulation between the condyle (rounded prominence) at the end of the mandible and the fossa (a concave depression) in the squamous portion of the temporal bone. The name of the joint is derived from the two bones which form the joint: the upper temporal bone which is part of the cranium, and the lower jawbone or mandible. The functions performed by this joint (chewing, swallowing, speaking, aesthetics, etc.) are performed with the association of several structures, such as masticatory muscles, craniomandibular ligaments, and nervous connections derived from V and VII cranial nerves. TMJ has three degrees of motion, which are activated while eating, talking, breathing, and even when changing horizontal or vertical position, producing an almost continuous functional demand on the TMJ. The volume of movement of the TMJ increases the likelyhood of pathological disorders. The effects on the TMJ due to pathological disorders usually are not apparent until later in the disease process. While RA may be the most frequent articular degenerative process of the TMJ, other articular degenerative processes can affect the TMJ, such as psoriac arthritis, systemic lupus, erythematous, gout, non-inflammatory diseases, ailments, trauma, muscle disorders, and the like. Articular degeneration of the TMJ typically leads to severe damage of the TMJ and pain. Patients may experience symptoms including deep and dull preauricular pain, headaches, myofascial pains, morning jaw stiffness, clicking, decreased bite form, difficulty in swallowing and showing, decreased jaw mobility and occlusal changes. In some scenarios, the condyle may erode, such as flatten, lose height, and/or lose volume. Further, the intra-articular pannus surrounding the articular disk may form and lead to destruction of the disk, condylar resorption and erosion of the fossa.
Degenerative disorders of the TMJ has typically been treated with anti-inflammatory drugs. However, once the temporomandibular joint has been compromised, surgical treatment is commonly a preferred or more effective option. TMJ implants have increased in demand as the amount of jaw joint and muscle disorders causing articular degenerative have increased. Current typical TMJ implants for articular degeneration face several deficiencies in both design and long-term performance. For example, evidence suggests that many of the failures of typical TMJ implants are related to defects in design and materials, rather than material fatigue as TMJ forces are relatively low (e.g., less than about 450 MPa) when compared to the strength of common implant materials (e.g., titanium or Cr—Co—Mo alloys).
Current TMJ implants or treatment devices typically mimic the “ball and socket” design of prosthetic hip implants. Specifically, current TMJ implants may consist of three components: a condylar or mandibular implant made of metal, a fossa implant made of metal or a hard plastic polyethylene, and metal screws that attach the condylar and fossa implants to the exterior surface of their corresponding bones. Many mandibular component designs are relatively similar in that they provide a plate portion for fixation to the mandible, and an articulation surface for abutment with the fossa component. The plate portion of the mandibular component is typically attached to the exterior of the mandible (i.e., lateral installation), such as against the outer lateral surface of the condyle with screws passing through fixation apertures of the plate portion.
Rotation and/or translation of the mandible with respect to the fossa (and therefore the corresponding components of current TMJ implants) is primarily provided by four muscles: the masseter, the medial pterigoid, the temporalis (activate for mouth closing), and the lateral pterygoid (activate for mouth opening). Each of the muscles apply different forces on the TMJ—and therefore to the fossa and mandibular components of typical TMJ implants. Analysis has shown that current TMJ implants cannot adequately or properly manage mechanical forces applied thereto by a patient's muscles. For example, current mandibular components and corresponding fixation screws of TMJ implants may not adequately address the stress distribution of the component.
Loads transmitted inferiorly to the top of typical mandibular components are transmitted from the mandibular component to the mandible through the screws fixing the mandibular component to the mandible. The first screw of the mandibular component in the superior-to-inferior direction is subject to the maximum stress. For example, the high von Mises stress of current mandibular components may vary between 106 and 126 MPa, and highest stress may be positioned adjacent to first screw. Common prior implants claim to compensate for the high stresses on the first screw by distributing the load over other screws. Regardless, however, the fixation screws of current TMJ implants transmit loads from the implant to the mandible bone and are the points where the maximum von Mises stresses are found. These high stresses on the fixation screws, especially on the first screw, fixing the mandibular component to the mandible commonly lead to failures of such current TMJ implants. Further, lateral installation of such exteriorly mounted mandibular components of current TMJ implants fails to provide functional ranges of motion of the joint that are similar to “normal” physiological parameters.
As a result, considering the state of the art that exists today, there is a need for better implants and methods for TMJ treatment that adequately support the stresses and loads of the temporomandibular joint to provide reliable, long-lasting treatment solutions that also allow for more functional ranges of motion.